Burner safety and scavenging control



Jan. 3, 1950 F. E. LANGE BURNER SAFETY AND SCAVENGING CONTROL Filed Aug.

97v goMae Patented Jan. 3, 1950 UNI-TED STATES PATENT OFFICE BURNER SAFETY AND SCAVENGING CONTROL Frederick E. Lange, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn.,,a'. corporation of Delaware Application August 11, 1945, Serial No. 610,264

' 12 Claims.

The present invention is concerned with burner control apparatus and more particularly apparatus of the type in which provision is made for operating a burner blower for a period of time after interruption of the fuel.

In many types of oil burner it is desirable that the blower or other means for delivering air to the burner be continued in operation for a period of time after the delivery of fuel is terminated. Sucha period of blower operation is often referredto as a blow out cycle. The reason for such a blow out cycle is that otherwise a few drops of oil tend to remain on the burner and due to the rather high temperature conditions existing in the furnace following a termination of burner operation, this oil becomes carbonized.

When the process is repeated as often as the burner is placed in operation, carbon tends to accumulate to a point where operation of the burner may be impaired. In order to provide for such continued operation of the blower after the fuel has been interrupted, various timing arrangements have been proposed. While satisfactory, these additionally complicate the control apparatus and add to the expense thereof. It has also been suggested that the flame responsive device can be employed to provide a timed period of blower operation following the interruption of fuel, such timed period of blower operation being equivalent in length to that required for the flame responsive apparatus to detect the presence of flame. The difficulty with such an arrangement is that in order to obtain a sufficiently long period of blower operation, it is necessary to have such a slow rate of response of the flame responsive apparatus that dangerous conditions may arise in the case of an abnormal flame failure.

An object of the present invention is to provide burner control apparatus in which the timing of the blow out cycle is performed by the flame responsive apparatus and in which the speed of response of the flame responsive apparatus is relatively rapid in the event of an abnormal flame failure.

A further object of the present invention is to provide burner control apparatus in which a safety cut out is provided, this safety cut out being operative only when the flame responsive apparatus does not indicate the presence of combustion. the flame responsive apparatus also normally being effective to maintain the blower in operation a predetermined period of time after the oil va-lve has closed following a termination of a call for heat, and in which the speed of re- 2 sponse of the flame responsive apparatus is much greater in the event of an abnormal flame failure than in the event of a normal flame failure following a termination of the call for heat.

A further object .of the present invention is to provide an arrangement such as set out in the previous object in which the flame responsive apparatus is effective to quickly terminate operation of both the blower and the fuel control in the event of an abnormal flame failure.

A further object of the present provide burner control apparatus such as set out in the previous objects in which the speed of response of the flame responsive apparatus is much more rapid during a call for heat by a main control device than upon a termination of the call for heat by the main control device.

A further object of the present invention is to provide an arrangement in which the flame responsive device employs electronic means.

A further object of the present invention is to provide an arrangement such as set out in the immediately preceding object in which the timing of the flame responsive means is changed by varying the time constant of a capacitive circuit in the flame responsive means.

Other objects of the present invention will be apparent from a consideration of the accompanying specification, claims, and drawings, in which Figurel is a schematic view of one form of my invention, v

Figures 2 and 3 areschematic views of relays employed in the apparatus of Figure 1, and

Figure 4 is a schematic view of a portion of a modification of my invention.

Referring to Figure 1, the burner apparatus to be controlled comprises a blower I0 employed to supply air under pressure to an atomizing type of oil burner, the nozzle of which is shown in the lower part of the figure and designated by the numeral II. The numeral H is employedtoim dicate an oil valve which controls the flow of fuel to the burner. This valve may, for example, be. of a solenoid type which is open whenever energized and closed when deen'ergized. Also included in the burner apparatus being controlled is an ignition means [2 which is associated with the burner nozzle It in such a manner as to ignite the oil mixture issuing from the nozzle. This ignition means may, for example, take the form of a high voltage transformer and spark electrodes adapted to produce a spark in the path of the mixture issuing from the nozzle.

The main control for the system with which my apparatus is employed is a thermostat l6.

invention is to This thermostat may, for example, be a room thermostat located in the space whose temperature is to be controlled or it may be a boiler water thermostat responsive to the temperature of the boiler water. The thermostat is shown as comprising a bimetallic element II to which is attached a contact arm ll adapted to sequentially engage with two contacts I! and 20. As indicated by the legend adjacent the thermostat, the bimetallic element I'l moves contact arm ll to the left upon a. drop in temperature. The contact arm II is so spaced from contacts l9 and 20 that it first engages contact I! and then upon a. further drop in temperature engages contact 20.

The thermostat ll controls the energization of a relay indicated in its entirety by the reference numeral ll. This relay comprises a relay coil Ila and a plurality of switch blades 25b, 25c, 25d, Ile, and llf. In order to simplify the showing the circuit, switch blade lle has been shown in a different portion of the drawing than switch blades 25b, 25c, and 25d. Moreover, switch blade II! has been shown on the opposite side or the relay coil from switch blades 25b to d. In order to illustrate the normal relationship between the elements of relay ll, the relay has'been shown with the elements in their normal relation in Figure 2. The relay switch blades Ilb to Ill are adapted to cooperate with contacts ily, 25h, 25k, 25m and Ilp, and Iln. respectively. The switch blades III), e, d. e, and j are biased out of engagement with contacts 25a, h, k. P, and n, respectively, and are adapted upon energization of the relay coil 25:: to be moved into engagement with those contacts. The switch blade He is biased into engagement with contact Ilm and is adapted upon energization of relay coil Ila to move out of engagement with that contact.

A thermal safety switch ll also controls the energization of relay ll. This safety switch may be of any type which at the end of a period of time moves to a circuit interrupting position and remains in that position until manually reset. A typical switch of this type which may be employed is that shown in the patent to John M. Wilson 2,290,399. As shown schematically in the drawing, the switch consists of a pair of switch blades ll and ll, the switch blade 31 being held in engagement with the switch blade 36 against its bias by a bimetallic element ll. An electric heater "is located adjacent bimetallic element ll and is eilective when energized to heat bimetallic element ll to cause it to warp to the right, as indicated by the legend adjacent the element ll. Upon continued energization of heater ll beyond a predetermined period of time the bimetallic element ll moves out from under switch blade 31, permitting switch blade 31 to drop away from switch blade ll. When this happens, the switch blades ll and I! must be manually reenmed.

Reference numeral ll is employed to generally designate a further relay. This relay comprises a coil lla and four switch blades llb, llc, d, and lle. Switch blade D is shown as separated from the remaining switch blades. The units of the relay are shown in their normal relationshipdn Figure 3. The switch blade llb cooperates with contacts ll! and lla. being biased into engagement with the latter contact andbeing moved into engagement with the former contact upon energization of relay coil a. The switch blades llc and "(1 cooperate with contacts llh and 1:, respectively, being biased out of engagement with those contacts and moved into engagement thereand moved into engagement with the latter upon energization of the relay coil Ila.

The energization of relay It is controlled by flame responsive apparatus including 'an electron discharge tube lll. This tube comprises an anode St, a grid 52, and a cathode ll. Associated with the cathode is a cathode heater ll. The three electrodes together with the cathode heater are enclosed in an envelope ll which may, for example, be evacuated. The tube 50 is supplied with power by a transformer 58, this transformer comprising a primary winding ll, a high voltage center tapped secondary winding ll, and a low voltage secondary winding l2. The secondary winding 62 is connected by conductors l3 and ll to the filament heater ll. The extreme left hand terminal of secondary ll is connected by conductors ll and ll to the right hand terminal of relay winding lla, the left hand terminal of which is connected by conductors l7 and ll to anode II. The center tapped secondary 6| is connected by conductor ll, resistor ll, and conductors ll and ll to the cathode l3. Thus, the left hand side or secondary II is employed as a source of plate potential for the anode circuit of tube 50.

The right hand side of secondary ll is employed to control the potential of grid 52. The extreme right hand end of secondary 8| is connected to grid 52 by conductors H and 12, resistor 13, condenser ll, conductors ll, ll, 11 and II, and resistor 19. A further resistor II and a further condenser ll are connected between conductor ll leading to the cathode I3 and conductor ll leading to the grid II. A third condenser ll is connected in parallel with condenser ll under certain conditions and in parallel with resistor ll under other conditions. When the relay Zl is deenergized so that switch blade lle is in engagement with contact Ilm as shown. the condenser I3 is in parallel with condenser ll. When, however, relay il is energized as during a normal burner operation, the condenser II is in parallel with resistor ll. The capacity of condenser ll is relatively large as compared with that of condenser l I. 1

Connected in parallel with resistor ll and condenser ll is a photoelectric cell It having an anode ll and a cathode II. The anode 89 is connected by conductors ll and I2 to the upper terminal of resistor II. The cathode ll is connected by conductor l2, resistor II, and conductors ll and ll to the lower terminal of condenser 14. The photoelectric cell II is mounted with respect to the flame of burner ll in such a manner as to be illuminated by it. The photoelectric cell II, when so illuminated, acts as a rectiiying impedance.

A condenser ll is connected in parallel with relay coil lla by conductors ll and l1. The function of condenser ll is to by-pass the A. 0. component of the pulsating current flowing through tube ll when the latter is conductive.

Power is supplied for energization of relay II by a step down transformer II. This transline voltage 88 and a low voltage primary winding 38. The

88 is connected by conductors III, III, I82, and I83 to line wires I04 and its leading to any suitable source of power (not shown).

Operation Before proceeding with the description of the apparatus as a whole, the operation of the flame responsive portion of the apparatus will first be considered. The operation of the flame detecting apparatus is fully set out in the copending application of John M. Wilson, Serial No. 465,476, filed November 13, 1942, issued as Patent No. 2,448,503, Aug. 31, 1948. While the operation is explained in the following paragraphs in sufficient detail to enable a full understanding of the same as far as its application to the present apparatus is concerned, reference is made to the above mentioned Wilson patent for a more detained understanding of the operation.

It will be assumed at first that the main burner is not ignited. Under these conditions, the current flowing through condenser 8| is that flowing through the following circuit: from the right hand terminal of secondary 8| through conductors II and I2, resistor 13, condenser 14, conductor ll, resistor 88, condenser 8|, resistor 84, and conductor 83 to the center tap of secondary 8|.

It will be assumed at first that the relay 25 is energized so that switch blade 25a is in engagement with cathode 259. Under these conditions, the condenser 83 is connected in parallel with resistor 84 by a circuit extending from the upper terminal of resistor 84 through conductor 10, contact 25p, switch blade 25c, conductor 81, condenser 83, and conductor 85 to the lower ter-,

minal of resistor 84. Since, as indicated above, the resistor 84 is in series with the cathode, the condenser 83, being in parallel with resistor 84, is

. likewise in series with the cathode. Thus, when current flows through the anode circuit, the condenser 83 assumes a charge equivalent to the voltage drop across resistor 84. When relay 25 is energized as is now being assumed, condenser 83 does not in any way affect the operation of condenser 8|. Thus, the voltage across condenser 8| is due solely to that of the circuit just traced. It will be recalled that the imp'edances in this circuit are all symmetrically conductive so that-any voltage across condenser 8| is an alternating voltage. Since the lower terminal of condenser 8|, which is the terminal connected to grid 52, is connected to the right hand terminal of secondary 8| which is 180 out of phase with respect to the left hand terminal, to which the anode is connected, it will be obvious that the alternating voltage across condenser 8| is 180 out of phase with the anode voltage. In other words, during the half cycles in which the anode 5| is positive with respect to the cathode, the voltage impressed across condenser 8| under the conditions being considered is of such polarity as to bias the grid 52 negatively with respect to the cathode 53. The tube 50 is thus sufllciently non-conductive as not to effectively-energize relay coil 40a.

Let it now be assumed that the photoelectric cell 88 is illuminated by a flame issuing from burner I4. Under these conditions, the photoelectric cell 88 is conductive so that a new circuit is established to condenser 8| as follows: from the right hand terminal of secondary 8| through conductors II and 3|, anode 88, cathode 8 88, conductor 92, resistor 83, conductors TI and I8, resistor 88, condenser 8|, resistor 84, and conductor 89 to the center tap of secondary 8|. Due to the rectifying characteristic of photoelectric cell 88, there is an appreciable current flow through the circuit just traced only in the direction in which it was traced. As a result, a charge tends to be impressed upon condenser 8| which is of such polarity as to cause the lower terminal of condenser 8| to tend to become positive with respect to the upper terminal. As previously pointed out, it is the lower terminal of condenser 8| which is connected to the grid 52. Hence, the.

effect of this charge is to raise the potential of grid 52 with respect to the cathode 53. The photoelectric cell and the constants of the circuit are such that with a normal burner flame the potential of grid 52 is raised to a point such that sufflcient current flows through tube 50 to cause effective energization of the relay 40a. The current flowing through the relay 40a flows through the following circuit: from the left hand terminal of secondary 8| through conductors and 88, relay coil 40a, conductors 81 and 88, anode 5|, cathode 53, conductors 88 and 85, resistor 84, and conductor 89 to the center tap of secondary 8|. The effect of the establishment of this circuit is to cause the effective energization of relay 48 so as to cause switch blades 40b, 40c, 40d, and 40e to move to their energized positions in which switch blades 40b, 48c, and 40d are in engagement with contacts 40!, 40h, and 40k and in which switch blades 40!) and 406 are out of engagement with contacts 409 and 40m.

In tracing the above circuit, it is to be noted that the circuit included the resistor 84. With relay 25 energized as has been assumed, condenser 83 is connected in parallel with resistor 84. Thus, with relay 25 energized and with the photoelectric cell 88 exposed to a flame, the condenser 83 becomes charged with a voltage equal in magnitude to that across resistor 84 and of a polarity such that the upper terminal of condenser 83 is negative with respect to the lower terminal. Upon relay coil 25 becoming deenergized, the condenser 83 is connected in parallel with condenser 8| by a circuit extending from the upper terminal of condenser 8| through conductor 85. condenser 83, conductor 81, switch blade 25c. contact 25m, and conductor 95. When the condenser 83 is so connected, the positive terminal of the condenser is connected to the lower terminal of condenser 8| which, as previously explained, is connected to the grid 52. Thus, the effect of this is to increase the charge across the condensers connected to the grid 52. This is effective following a normal shut down to maintain the grid at a raised potential with respect to the cathode 53 longer than would otherwise be the case since it is necessary for both condensers 8| and 83 to lose the unidirectional component of the voltages across them.

It is to be pointed out that the electronic apparatus which I employ is responsive only to a can:

, Ill and Ill, safety switch heater ll, conductor IlI, relay coil llb, and conductor Ill to the left hand terminal oi secondary ll. The result of the establishment of this circuit is to cause the energization 01' relay coil lla with the resultant movement of switch blades llb, llc, lld, lle,

and llf into engagement with contacts 259, 25h, lllc, llp, and lln, respectively. At the sam time, switch blade lie is moved out of engagement with contact llm.

The engagement of switch blade lid with contact 251: results in the establishment of a holding circuit to relay coil lla as follows: from the right hand terminal of secondary 99 through conductor II 5, safety switch blades 31 and ll, conductor I ll, contact Il, contact arm Il, bimetallic element I'I, conductor Ill, switch blade lld, contact llk, conductor Ill, heater ll, conductor Ill, relay coil lla, and conductor Ill to the left hand terminal of secondary ll. It is to be noted that the circuit just traced is independent of contact ll, the last to be engaged of the thermostatic contacts. This insures that the relay ll willremain energized until there has been a rise in temperature suillcient to separate thermostat blade I 8 from contact Il. In this way, provision is made for a diilerential in temperature between It is also to be noted that the holding circuit just traced is independent of the out contact llg of relay ll. It was desirable that the original energizing circuit include such an out contact to protect against the system being accidentally brought into operation with relay ll in its energized position. If it were possible to initiate operation of the system with the relay in thi position, there would be no assurance that the relay was not accidentally retained in this position even though flame were not present. There would thus be no provision for checking the establishment of flame.

' The engagement of switch blades ll! and llb with contacts lln and llg, respectively, results in the establishment oi the following energizing circuit to the ignition Il: from line wire Ill through conductors IlI, Ill and Ill, contact lln, switch blade llj, conductor Ill, switch blade llb, contact llc, conductor Ill, contact llg, switch blade llb, conductors Ill, Ill, Ill, and Ill, contact llm, switch blade lle, conductor Ill, ignition I2, and conductors Ill, Ill, Ill, Ill, Ill, and Ill to the other line wire Ill. A circuit is also established to the primary winding ll of the transformer ll as follows: from line wire Ill through conductors Ill, Ill, and Ill, contact lln, switch blade ll], conductor I, switch blade llb, contact llc, conductor IlI, contact lla, switch blade llb, conductors Ill, Ill. Ill, and Ill, primary winding ll, and conductors Ill, IlI, Ill, Ill, Ill, and Ill back to the other line wire Ill. The establishment of the circuit Just traced results in energization of the electronic apparatus with the result that the cathode heater ll starts to warm up to place the apparatus in condition to check the operation of the flame The movement 0! switch blade llc out of engagement with contact llm, as a result of the energization of relay ll, results in condenser ll being disconnected from condenser lI. Since condenser M has a relatively small capacitance. the time required for charging the condenser is relatively small as compared with that when condensers 8i and 83 were in parallel. Thus, instead of from one to three minutes being required, the charging time may be a matter 01' only a comparatively few seconds. Thus. as soon as the cathode heater is warmed up, electronic apparatus is capable of detecting very rapidly the establishment of combustion at the main burner.

At the same time as the circuits are established to the ignition means Il and the primary 0! the transformer ll, circuits are also established to the blower II and the oil valve II. The circuit to blower Il is as follows: from line wire Ill through conductors IlI, Ill, and Ill, contact lln, switch blade llf, conductor Ill, switch blade llb, contact llc, conductor Ill, contact llg, switch blade llb, conductors Ill, ill, and Ill, blower II, and conductors IlI, Ill, Ill, Ill, and Ill to the other line wire Ill. The circuit established to oil valve II is as follows: from line wire Ill through conductors Ill, Ill, and Ill, contact lln, switch blade llj, conductor Ill,

switch blade llb, contact llc, conductor III, I

contact lla, switch blade llb, conductors Ill and Ill, contact llh, switch blade llc, conductor Ill, oil valve II, and conductors Il'I, Ill, and Ill to the other line wire Ill.

As a result 01 the circuits traced above, the oil valve is energized to deliver oil to the burner. the blower is in operation, the ignition means is functioning, and the flame responsive apparatus is capable of detecting the presence of flame. Normally, the burner ignites almost immediately so that as soon as the flame responsive apparatus has warmed up, a matter requiring considerably less than a minute, the flame responsive apparatus responds to the presence 01' flame by causing energization of relay lla with the movement of switch blades llb, llc, lld, and lie to their energized positions previously referred to.

The movement of switch blade llb into engagement with contact ll! results in a shunt being established around the heater ll of the safety switch ll, this shunt extending from the upper terminal of heater ll through conductors Ill and Ill, switch blade llb, and contact ll! to the lower terminal of heater ll. The eil'ect of the establishment of this circuit is to termihate the operation of the safety switch ll. It heater ll were allowed to remain energized sumciently long. safety switch ll would eventually open to cause deenergization of relay ll and as a result the rest 0! the apparatus. By establlshing the shunt around heater ll, however, the bimetal element cools down so that it is not eiiective to interrupt operation 01' the system.

The movement 01'- switch blade lle out of engagement with contact llm interrupts the circuit to the ignition Il. Since the main burner has been ignited, the continued operation of the ignition is no,longer The movement of switch blade' lld into engagement with contact It results in the establishment of the following circuit to blower III:

from line wire Ill through conductors Ill, Ill.

m, and m, contact llk, switch blade lld, con-' ductors Ill, Ill, Ill, and Ill, blower Il, con,- ductors llI, Ill, Ill, Ill, and Ill back to the I04. It is to be noted that the new circuit parallels switch blades 25], 45b, and 25b and is not dependent upon either relay 25 or relay 5. In other words, the closure of switch blade 400! with contact 401: results in the establishment of a shunt circuit between conductor I28 and switch blade 25!) as follows: from conductor I28 through conductor I8I and I52, contact 4070, switch blade 40d, and conductors I83, I46, I35, I34, and I33. Since the left hand terminal of ignition, transformer 80 is connected to conductor I", it will be apparent that the ignition transformer is now also energized through switch blade 40d and contacts "is independently of relays 25 or 45. Similarly, since the oil valve II is connected through switch blade 25c and contact 25h to conductor I33, it will be apparent that this device is now also energizedv independently of relay 45. Since, however, it includes in its circuit switch blade 25c, its energization is dependent upon the continued energization of relay 25.

other line wire nected in parallel with condenser 8I. Since, as previously explained, the condenser 83 has by reason of its parallel connection with resistor 84 assumed a charge of such polarity that the lower terminal of condenser 83 is positive with respect 7 through it is interrupted. The voltage across con- The movement of switch blade 400 into engagement with contact 40h results in the establishment of an energizing circuit to relay coil 45a as follows: from line wire I05 through conductors IOI, I28, and ISI, switch blade 00, contact 40h, conductor I10, relay coil 45a, and conductors III, I43, I, and I03 to the other line wire I04. The energization of relay coil 45a results in switch blade 45h moving out of engagement with contact 450 and into engagement with contact 45d.

The movement of switch blade 45b out of engagement with contact 450 interrupts the previously traced circuits under the control of relay to the blower, oil valve, and ignition transformer. Since, however, new circuits under the control of relay 40 have already been established, this does not terminate energization of these devices.

The movement of switch blade 45!) into engagement with contact 45d results in a holding circuit being established for relay coil 45a as follows: from line wire I05 through conductors IOI, I28, and I29, contact 2511, switch blade 25f, conductor I30, switch blade 45!), contact 4511, conductor I13, relay coil 45a, and conductors III, I43, I, and I03 to the other line wire I04. This holding circuit is independent of relay 40 and insures that the relay 45 will remain energized as long as relay 25 is energized.

The apparatus is now operating normally. The oil valve and blower are both energized and the safety switch heater 39 and the ignition I2 are deenergized. The flame responsive apparatus is not only energized, but due to the disconnection of the condenser 83 from the condenser 8I, the speed of the response of the flame detecting apparatus is relatively rapid. Under normal conditions, the burner will continue to operate until the temperature surrounding the thermostat I6 rises to a point where thermostat contact arm I8 has moved out of engagement with not only contact 20 but also contact I8. When this happens, the relay 25 is immediately deenergized so as to cause movement of the switch blades thereof to their deenergized positions.

The movement of switch blade 250 out of engagement with contact 25h results in the immediate deenergization of the oil valve II. This interdenser 8| now tends to assume the alternatlns value originally considered. This tendency is resisted, however, by the inclusion of condenser 83 in parallel with it, which condenser is of relatively large capacity and has a substantial positive voltage across its terminals. Because of the inclusion of condenser 83 in parallel with condenser 8I, the apparatus requires a substantial period of time, for example, a minute, in order to cause deenergization of relay 00a.

As long as relay 48 is energized, the blower continues in operation. Due to the delay in the response of the flame responsive apparatus by reason of the connection of the condenser 83 in parallel with condenser 8I, this operation of the blower continues for a substantial period of time after deenergization of the fuel oil valve II. This period of time is adequate to remove any traces of oil remaining at the burner.

The movement of switch blade "I out of engagement with contact 251:. results in the interruption of the holding circuit to relay coil 480. When relay 40 becomes deenergized the circuit to coil a is broken at 4071. and relay 45 moves to the deenergized position shown in the drawing.

As soon, therefore, as relay 0 is deenergized as a result of the flame responsive apparatus detecting the extinguishment of combustion, all of the elements have returned to the position shown in rupts the delivery of fuel to the burner. At the the drawing in which the apparatus is again in condition for the initiation of a new cycle of operation as soon as the thermostat I8 calls for heat.

In considering the operation above, it was assumed that combustion was established at the main burner in the normal manner and continued throughout the call for heat by the room thermostat. Let it be assumed first, however, that combustion is never established. Under these conditions, the flame responsive apparatus does not cause energization of relay 0 with the result that the shunt circuit around heater 33 is not established by the movement of switch blade 40?) into engagement with contact 401. Accordingly, the heater 38 continues to heat the bimetallic element '38 of safety switch 35 until the element 38 moves to the right beyond switch blade 31 allowing switch blade 31 to separate from switch blade 38. This resultsin the interruption of the circuit to relay 25 and the resultant deenergization of that relay to cause complete deenergization of the entire system. Before it can again be placed into operation, it is necessary for the switch blade 31 to be manually raised into engagement with switch blade 36. Before doing so, the attendant can inspect the apparatus to determine the cause of the failure to establish combustion.

Let it be assumed now that combustion is properly established but that for some reason or other a combustion failure occurs before the'termination'of the call for heat. Under these conditions, the photoelectric cell 38 becomes non-conductive so that the only energizing circuit for condenser II is that which was first traced and which, it

will be recalled, includes only symmetrically con- .ductive impedances. Thus, in a very short period of time, for example, a matter of only a few seconds, the condenser 8| loses the positive charge resulting from the action of photoelectric cell 88 so that the only voltage across it is the alternating voltage first considered. It will be recalled that this alternating voltage biases the grid. negatively to such an extent that the relay a is non-,

conductive. It is to be noted that under these circumstances condenser 83 is not in parallel with condenser 8i but rather is in parallel with resistor 84. Since resistor I4 is not connected between the cathode and grid, the condenser it, when connected in parallel with resistor 84, does not appreciably affect the voltage applied to grid 52. It certainly does not aifect the operation of condenser 8|. Thus, the r sponse of the condenser BI to the extinguishment of the burner flame is extremely rapid under these conditions.

As soon as relay 4. is deenergized, the oil valve, the blower, and the transformer I are all immediately deenergized. This is due to the fact that relay 45 is still energized so as to hold switch blade 45b out of engagement with contact "c. Thus, the originally traced circuits under the control of relay are interrupted so that the only circuits which would otherwise exist would be those resulting from the closure of switch blade "d with contact it. Thus, when switch blade 40d separates from contact k, all of the circuits to the burner apparatus are interrupted.

The separation of switch blade b from contact f as a result of the deenergization of relay 40 interrupts the shunt circuit around heater II so that the heater 39 again starts heating the safety switch. Thi operation will continue until the safety switch opens its contacts to deenergize relay 25. when this happens, switch blade 25! will separate from contact 251i to interrupt the holding circuit for relay coil 45a to cause deenergization of relay 45. Again, all of the apparatus will be completely deenergized and a manual resetting of the safety switch will be required before the system can again be placed into operation.

It is to be noted from the above operation that the response of the flame apparatus following a termination of a call for heat is relatively slow so as to maintain the blower in operation for a predetermined period of time following the closure of the fuel oil valve. When, however,there is a flame failure while the main burner control is in operation, the flame responsive apparatus responds quickly to the extinguishment of flame and causes an immediate closure of both the oil valve and the blower. Thus, the apparatus of my invention utilizes a flame responsive apparatus to provide a timed period of blower operation following the fuel interruption without in any way reducing the sensitivity of the flame responsive apparatus to an abnormal flame failure. This is obviously highly desirable since when there is an abnormal flame failure, it is imperative that the delivery of oil be interrupted immediately.

Species of Figure 4 the present case,

of the flame responsive apparatus. Since the main portion of the burner control apparatus is identical to that of Figure 1, it has not been 11-- lustrated in Figure 4. Furthermore, to facilitate a comparid'orr-of Figures 1 and 4, the same reference characters have been used in Figure 4 to indicate elements which are identical to those of Figure. l. The primary difference between Figure 4 and Figure 1 is that the change in response is accomplished by varying the amount of resistance connected in series with condenser II. In two resistors I10 and I1! have been connected in series with condenser II in lieu of resistor ll of the species 'of Figure 1-. The resistor I10 has a relatively large resistance as compared with that of resistor I15. The out contact 25m of relay 25 has been eliminated so that the switch blade 25c cooperates only with contact 25p which it engages when the relay 2! is energized. When the relay 2! is energized, the relatively large resistor I" is shunted out by conductor I16, contact 25p, switch blade "e, and conductor I11. Thus, whenever the relay 2| is energized, resistor I'll is effectively out of the circuit. Since resistor 84 is not employed in the present species, the shunting of resistor I1. results in resistor I15 being the only resistor between condenser 8| and the center tap of secondary GI. Furthermore, the total resistance now in series with condenser 8| is equal to the resistances of resistors 13 and I15, both of which have very small resistance values as compared with that ofresistor I10. As is well known, the time required for a condenser to discharge is dependent upon the time constant of the circuit which is proportional to the product of the resistance and capacitance in the circuit. By shunting out a large portion of the resistance, the time constant of the circuit is reduced so that the apparatus is able to respond quickly to the presence or loss of flame.

It will be apparent that the operation of the flame responsive apparatus is generally similar to that of Figure l as far as the operation of the burner system is concerned. As long as relay 25 is energized as is the case when thermostat II is calling for heat, switch blade He is engaged with contact 25p and shunts out resistor I" to render the apparatus quickly responsive to the presence or absence of combustion. As soon, how ever, as the thermostat is satisfied. the switch blade He moves out of engagement with contact 259, interrupting the shunt circuit around resistor I10 so that the time constant of the circuit including condenser 8| is increased to such a point that the response of the flame responsive apparatus is relatively slow. By proper choice of constants, the apparatus can be designed to require at least a minute to respond to the absence of a flame under theseconditions. This results in the blower continuing in operation for a substantial period of time following the closure of the fuel oil valve.

While I have shown certain specific embodiments of my invention for purposes of illustration, it is to be understood that the scope of the invention is to be limited only by the appended claims. l

I claim as my invention:

1. Burner control apparatus including a fuel control; a burner blower; a safety cut-out; means adapted to respond to the presence of combustion at the burner being controlled; means ineluding a main control device for initiating operation of said fuel control, said burner blower, and said safety cut-out; means including said safety cut-out effective at the end of a timed period to terminate operation of said fuel control and burner blower unless the operation of a an;

13 said safety cut-out is previousl. interrupted: means including saldcombusti n responsive means for interrupting operation of said safety cut-out upon "the establishment of combustion and for again starting its operation if combustion is terminated; means effective upon the operation of said fuel control being terminated dueto said main control device assuming a position in which fuel is not demanded to continue the operation of said blower until said combustion responsive means responds to the termination of combustion; and means controlled by said main control device for causing said combustion responsive means to respond more quickly when said main control device is calling for burner operation than when it is not.

2. Burner control apparatus including a fuel control; a burner blower; means including a main control device for initiatin operation of said fuel control and burner blower when said main control device is in a position demanding burner operation; means effective when said main control device assumes a position in which burner operation is not desired to cause said fuel control to assume a fuel interrupting condition; means including flame responsive apparatus for continuing operation of said blower until said flame responsive apparatus has responded to the termination of burner flame; means including said flame responsive apparatus effective in the event of a flame failurewhile said main control device is calling for burner operation to cause said fuel control to assume a fuel interrupting position; and means to cause said flame responsive apparatus to respond more quickly to the termination of flame when said main control device is calling for burner operation than when it is not.

3. In a burner control apparatus; a burner; a main control device movable between heat demanding and satisfied positions; means for initiating delivery of fuel and air to said burner when said main control device is in heat demanding position and for interrupting said delivery of fuel when said control device assumes a heat satisfied position; means including a flame responsive apparatus for interrupting delivery of fuel while said control device is in its fuel demanding position upon the occurrence of a flame failure; means including said flame responsive apparatus effective upon said control device assuming its satisfied position to continue delivery of air to the burner until said flame responsive apparatus has responded to the extinguishment of the burner flame; and means to decrease the speed of response of said flame responsive apparatus upon said main control device becoming satisfied.

4. In a burner control apparatus; a burner; a main control device movable between heat demanding and satisfied positions; means for initiating delivery of fuel and air to said burner when said main control device is in heat demanding position and for interrupting said delivery of fuel when said control device assumes a heat satisfied position; means including a flame responsive apparatus for interrupting delivery of fuel and air while said control device is in its fuel demanding position upon the occurrence of a flame failure; means including said flame responsive apparatus effective upon said control device assuming its satisfied position to continue de-' livery of air to the burner until said flame responsive apparatus has responded to the extinguishment of the burner flame; and means to decrease the speed of response of said flame responsive apparatus upon said main control device becoming satisfied.

5. In a burner control apparatus; a burner; a main control device movable between heat demanding and satisfied positions; means for initiating delivery of fuel and air to said burner when said main control device is in heat demanding position and for interrupting said delivery of fuel when said control'device assumes a heat satisfied position; means including a safety controller effective after a timed period of operation of said safety controller to interrupt delivery of fuel to said burner; means including flame responsive apparatus for interrupting operation of .saidsafety controller upon the establishment of combustion within said timed period; means including said flame responsive apparatus effective upon said control device assuming its satisfied position to continue'delivery of air to the burner until said flame .responsive apparatus has responded to the extinguishment of the burner flame; and means to decrease the speed of response of said flame responsive apparatus upon said main control device becoming satisfied.

6. In a burner control apparatus; a burner; a main control device movable between heat demanding and satisfied positions; means for initiating delivery of fuel and air to said burner when said main control device is in heat demanding position andfor interrupting said delivery of fuel when said control device assumes a heat satisfied position; means including a safety controller effective after a timed period of operation of said safety controller to interrupt delivery of fuel and air to said burner; means including flame responsiveapparatus for interrupting operation of said safety controller upon. the establishment of combustion within said timed period; further means including said flame responsive apparatus for interrupting delivery of fuel while said control device is in its fuel demanding position upon the occurrence of a flame failure; means including said flame responsive apparatus effective upon said control device assuming its satisfled position to continue delivery of air to the burner until said flame responsive apparatus has responded to the extinguishment of the burner flame; and means to decrease the speed of response of said flame responsive apparatus upon said main control device becoming sat sfied. v

'7. In a burner control apparatus; a burner; a main control device movable between heat de- 5 manding and satisfied positions; means for initiatingdelivery of fuel and air to said burner when said main control device is in heat demanding position and for interrupting said delivery of fuel when said control device assumes a heat satisfled position; flame responsive apparatus including a condenser, a flame responsive element, and means including a. charging circuit for charging said condenser in accordance with the presence or absence of combustion adjacent said flame responsive element; means including said flame responsive apparatus for interrupting delivery of fuel while said control device is in its fuel demanding position upon the charge of said condenser assuming a predetermined value as a result of flame failure; means including said flame responsive apparatus effective upon said control device assuming its satisfied position to continue delivery of air to the burner until the charge of said condenser assumes said predetermined value due to the extinguishment of the manding position and for interrupting said de-.

livery of fuel when said control device assumes a heat satisfied position; flame responsive apparatus including a condenser and means for charging said condenser in accordance with the presence or absence of combustion adjacent said flame responsive element; means including said flame responsive apparatus for interrupting delivery of fuelwhile said control device is in its fuel demanding position upon the charge of said condenser decreasing below a predetermined value as a result of flame failure; means including said flame responsive apparatus effective upon said control device assuming its satisfied position to continue delivery of air to the burner until the charge of said condenser assumes said predetermined value due to the extinguishment of movement of said main control switch to heat demanding position and to maintain said blower energized until said combustion responsive means has responded to the termination of combustion adjacent the burner; means controlled by said switching means and connected in said fuel control circuit means for interrupting said fuel controlcircuit means when said combustion responsive means responds to the termination of combustion; and means effective when said apparatus is so connected to such a main control switch to cause said combustion responsive means to respond more quickly to the termination of combustion when said main control switch is in heat demanding position than when it is in its satisfied position.

11. Burner control apparatus for controlling a burner fuel control and a burner blower; said apparatus comprising: a relay; energizing circuit means for said relay adapted to be connected to a main control switch and to energize said relay when so connected and when said main control of the burner flame; and means effective upon said main control device moving to satisfied position to connect a further charged condenser in parallel with said first .named condenser to increase the time required for said first named v condenser to discharge. a

9. In a burner control apparatus; a burner; a main control device movable between heat demending and satisfied positions; means for initiating delivery of fuel and air to said burner when said main control device is in heat demanding position and for interrupting said delivery of fuel when said control device assumes a heat satisfied position; flame responsive apparatus including a condenser, a flame responsive element, and means including a charging circuit for charging said condenser in accordance with the pres- .ence or absence of combustion adiacent said flame responsive element; means including said flame responsive apparatus for interrupting delivery of fuel while said control device is in its fuel demanding position upon the charge of said condenser decreasing below a predetermined value as a result of flame failure; means including said flame responsive apparatus efl'ective upon said control device assuming its satisfied position to continue delivery of air to the burner until the charge of said condenser assumes said predetermined value to the extinguishment of the burner flame; and means effective upon said main control device becoming satisfied to increase theresistance of saidcharging circuit to increase the time required for said condenser to discharge.

10. Burner control apparatus adapted to be connected to a burner fuel control, a burner blower, and a main control switch movable between heat demanding and satisfied positions: said apparatus comprising: switching means; combustion responsive means adapted to be responsive to combustion conditions at a. burner to operate said switching means; fuel control circuit means effective when said apparatus is so connected to maintain said fuel control in fuel supplying position only while said main control switch is in heat demanding position; blower circuit means controlled 'by said switching means and adapted when said apparatus is so connected to initiate energirntion or the blower as a result switch is closed; further switching means, combustion responsive means adapted to be responsive to combustion conditions at a burner to operate said switching means; fuel control circuit means controlled by said relay and adapted to f be connected to a fuel control for the burner for maintaining said fuel control in fuel supplying position only while said relay is energized, blower circuit means controlled by said 'relayland said further switching means and adapted to be connected to a burner blower for initiating energization of the blower as a result of e rsization of the relay and for maintaining said blower energized until said combustion responsive means has responded to the termination of combustion adjacent the burner, means controlled by said further switching means and connected in said fuel control circuit means for interrupting said fuel control circuit means when said combustion responsive means responds to the termination of combustion, and means controlled by said relay to cause said combustion responsive means to respond more quickly to the termination of combustion when said relay is energized than when said relay is deenergized.

12. Burner control apparatus adapted to be connected to a burner fuel control, a burner blower, and a main control switch movable between heat demanding and satisfied positions; said apparatus comprising: switching means; combustion responsive means including a condenser for operating said switching means when the charge-across said condenser assumes a predetermined value; a flameresponsive element, and a charging circuit for charging said condenser in accordance with the presence or absence of combustion adjacent said flame responsive element; fuel control circuit means effective when said apparatus is so connected to maintain said fuel control in fuel supplying position only while said main control switch is in heat demanding position; blower circuit means controlled by said switching means and adapted when said apparatus is so connected to initiate energiration of the blower as a result of movement of said main control switch to heat demanding position and A to maintain said blower energized until said combustion responsive means has responded to the termination of combustion adjacent the burner; means controlled by said switching means and connected in said fuel control circuit means for interrupting said fuel control circuit means when said combustion responsive means m to the termination of combustion; and means eii'ective when said apparatus is so connected to such a Um STATES PATENTS main control switch to increase the time constant N r Name Date of said charging eircuitto decrease the speed 1,7 ,1 4 SWeott Oct. 15, 1929 of response of said combustion responsive means 5 71 Craso May 27, 1941 when said main control switch moves from its 2,299,501 schnleder fl' 1942 heat demanding position to its satisfied position. 3 R char 8% 81 D 1942 FREDERICK E. LANGE. 2,353,893 sponzenberz et 8!. Feb. 6, 1945 2,379,871 Benn, et ll July 10, 1945 REFERENCES CITED 1o The following references are of record in the tile of this patent: 

